Researchers at the U.S. Department of
Energy’s Lawrence Livermore National Laboratory have achieved a milestone in
materials science and electron microscopy by taking a high-resolution snapshot
of the transformation of nanoscale structures. Using the lab’s dynamic
transmission electron microscope (DTEM), Judy Kim and colleagues peered into
the microstructure and properties of reactive multilayer foils (also known as
nanolaminates) with 15-nanosecond-scale resolution.

“This is the first time that a detailed study of these reactive nanolaminates
has exposed what is happening in the self-propagating high-temperature
synthesis zone,” Kim said.

Time-resolved images of nanolaminates show a brief change in structure with a
short cellular phase separation during cooling. Observing short-lived behavior
(i.e., how a chemical reaction, structural deformation or phase transformation
occurs) is not easy, but is key to understanding many of the basic phenomena at
the heart of materials science, chemistry and biology. The ability to directly
observe and characterize these complex events leads to a fundamental understanding
of properties such as reactivity, stability and strength, and helps in the
design of new and improved materials and devices.

Unprecedented Imaging

Transmission electron microscopy (TEM) has evolved dramatically in
recent years and can spatially resolve microstructural details of phase and
structure, but it can’t collect in increments of less than a millisecond.
That’s where Livermore’s DTEM comes in. It provides scientists with the ability
to image transient behavior with an unprecedented combination of spatial and
temporal resolution: nanometers and nanoseconds.

“Direct real-space observations of phase transformations on the nanosecond
scale have allowed us to relate the formation mechanism in reactive multilayer
foils to binary alloy solidification,” Kim said. “This conclusion is based upon
transient features that could not have been found using any other technique.”

Because the team needed access to time and real-space that is impossible to
study using traditional methods such as conventional in situ TEM (limited to video
rates) or ultra-fast diffraction (which presently lacks direct real-space
imaging capabilities), the DTEM fit the bill.

“The ability
to determine not only crystal structure but also morphological evolution of
dynamic events on the nanoscale has far-reaching implications for the study of
materials science, non-equilibrium processes and the behavior of matter on very
fine scales of length and time,” Kim said.

Other Livermore researchers involved in the project include Thomas LaGrange,
Bryan Reed, Mitra Taheri, Michael Armstrong, Wayne King, Nigel Browning and
Geoffrey Campbell. The research first appeared in the September 12 edition of
the journal Science.